The invention relates generally to electrically shielded housings for electrical components and methods therefor.
Electrical devices are commonly mounted in housings made from non-conductive materials like plastics. The increasingly widespread use of electrical devices in noisy electrical environments however requires that the devices be shielded from electromagnetic interference, particularly radio frequency interference. In the automotive industry, for example, low voltage micro-controllers, pressure sensors, electric power steering devices and other noise sensitive electrical devices are employed increasingly in or near the engine compartment where shielding from electromagnetic interference, otherwise referred to herein as electrical noise or interference, is required. Unfortunately, non-conductive housings alone provide no electrical shielding for the electrical devices mounted or housed therein.
It is known in some applications to insert mold or otherwise dispose a stamped or extruded metal lining in a plastic housing cavity to provide electrical shielding for an electrical device subsequently mounted therein. See for example, U.S. Pat. No. 5,704,117 entitled xe2x80x9cMethod Of Assembling An EMI Shield Around An Electronic Componentxe2x80x9d. The stamped metal lining however constitutes an exposed conductive surface in the housing cavity that presents a hazardous condition for short circuiting electrical devices mounted therein. The metal lining components arc also relatively costly to manufacture and substantially increase housing weight. There are also sever limitations on the extent to which metal may be stamped or extruded to define intricate structural features, and for use in increasingly small housing cavities, resulting generally from the shear and tensile strength of the metal.
It is also known to apply a conductive ink onto a surface of a plastic housing cavity, for example in a spraying operation. Applying a conductive ink however generally requires some masking of the housing or cavity to prevent overspray, which is a laborious and costly procedure. Also, it is difficult to electrically connect a wire or lead to a conductive ink applied to the housing surface for grounding purposes. The conductive ink also forms an exposed conductive surface in the housing cavity that may short circuit electrical devices disposed therein, as discussed above.
It is also known to co-inject conductive and non-conductive plastics to form a plastic housing having an electrically shielded cavity The conductive plastic is loaded with a conductive material and forms a conductive lining in the housing cavity. The co-injection process however is not used widely, and has several disadvantages, including difficulty in grounding the conductive plastic lining and limitations on the thinness and dimensions thereof. The conductive plastic lining also has an exposed conductive surface, which is undesirable as discussed above.
It has been proposed to insert mold a relatively thin plastic lining, made conductive by a conductive filler material, in a plastic housing cavity for an electrical device. The plastic lining however is only suitable for static charge dissipation, not electrical shielding, since there is a severe limit on extent to which it may be made conductive by the conductive filler material. The plastic lining moreover must be formed separately in a prior molding operation, which is costly and complicated by the required thinness of the plastic lining. Additionally, the amount of conductive filler material required to make the plastic lining sufficiently conductive for static charge dissipation renders the plastic lining too brittle, and thus subject to failure. Also, the conductive plastic lining forms an exposed conductive surface on the housing cavity that presents a hazard for short circuiting electrical devices disposed therein as discussed above.
It is also known to manufacture electrically shielded plastic housings for electrical devices in thermal vacuum forming processes. In one known process, a non-woven conductive layer of tin and bismuth fibers is laminated onto a plastic sheet during a thermal vacuum forming process. The thermal vacuum forming process however is not generally capable of very well defining intricate structural features as is required in increasingly small housings. There are also additional costs associated with the lamination of the conductive layer on the plastic sheet, which is usually performed manually, and is otherwise not suitable for high production operations. The conductive fibrous layer also forms an exposed conductive surface on the housing cavity that may short circuit an electrical device disposed therein as discussed above.
The present invention is drawn toward advancements in the art of electrically shielded housings for electrical devices.
An object of the invention is to provide novel electrically shielded housings and methods therefor that overcome problems in the art.
Another object of the invention is to provide novel electrically shielded housings and methods therefor that are economical.
Another object of the invention is to provide novel electrically shielded housings having a cavity for receiving an electrical device and methods therefor that insulate the electrical device from the electrical shielding.
A further object of the invention is to provide novel electrically shielded housings and methods therefor comprising an insert member, formed preferably in a thermal forming operation, insert molded with a non-conductive body member to provide an electrically insulated and electrically shielded housing cavity for an electrical device.
Yet another object of the invention is to provide novel electrically shielded housings and methods therefor comprising insert molding a partially formed insert member with a non-conductive body member to provide an electrically insulated and electrically shielded housing cavity for an electrical device, whereby the partially formed insert member takes the exact intricate detail of a mold cavity during the inserting molding operation.
A further object of the invention is to provide novel electrically shielded housings and methods therefor comprising an at least partially formed insert member having a conductive inner surface portion and a non-conductive outer surface portion that may be assembled with a non-conductive body member, preferably in an insert molding operation, to provide an electrically insulated housing cavity that electrically shields an electrical device disposed therein.
A more particular object of the invention is to provide novel electrically shielded housings and methods therefor comprising generally an insert member disposed in a cavity of a non-conductive housing body member. The insert member includes a conductive inner surface portion disposed adjacent an outer surface portion of the body member cavity. A non-conductive outer surface portion of the insert member forms a housing cavity for receiving an electrical device. The conductive inner surface portion of the insert member at least partially electrically shields the electrical device, and the non-conductive outer surface portion of the insert member insulates the electrical device from the conductive inner surface portion thereof.